In recent years, with higher function and diversification of various types of electronic devices such as portable telephones and electronic cameras, use of such devices in which a light-transmissive touch panel is attached to a front surface of a display element such as a liquid crystal display element and the touch panel is pressed with a finger or a pen while looking at the display of the display element on the rear surface through the touch panel to switch among various functions of the device is increasing, where a touch panel that is inexpensive and that enables various operations is desired.
Such a conventional touch panel will be described with reference to FIGS. 7 to 9C. In the drawings, the dimension is shown in a partially enlarged manner to facilitate the understanding of the configuration.
FIG. 7 is a cross-sectional view of a conventional touch panel. FIG. 8 is an exploded perspective view of the conventional touch panel. In FIGS. 7 and 8, the touch panel includes upper substrate 1, upper conductive layer 2, a pair of upper electrodes 3A, 3B, lower substrate 4, lower conductive layers 5, lower electrodes 6, spacer 7, and wiring substrate 8. Upper substrate 1 has a film shape and has a light transmitting property. Upper conductive layer 2 is formed to a substantially rectangular shape over substantially the entire surface of the lower surface of upper substrate 1. Upper conductive layer 2 is made of indium tin oxide, for example and has a light transmitting property. A pair of upper electrodes 3A and 3B are formed at a front end and a back end of upper conductive layer 2. The ends of upper electrodes 3A and 3B are extended to the front end of upper substrate 1.
Lower substrate 4 has a film shape or a plate shape, and has a light transmitting property. The plurality of lower conductive layers 5 are formed to a substantially strip form on the upper surface of lower substrate 4. The plurality of lower conductive layers 5 are made of indium tin oxide, for example and have a light transmitting property. A plurality of dot spacers (not shown) are arranged at predetermined intervals on the upper surfaces of lower conductive layers 5. Lower electrode 6 is formed at the front end of each lower conductive layer 5. An end of lower electrode 6 is formed to extent to the front end of lower substrate 4.
Spacer 7 is formed at the inner edge of the outer periphery between upper substrate 1 and lower substrate 4. Spacer 7 is formed to a substantially frame shape. Spacer 7 is formed by applying an adhesive (not shown) on upper and lower surfaces or on one surface to laminate the outer peripheries of upper substrate 1 and lower substrate 4. Upper conductive layer 2 and lower conductive layer 5 thereby face each other across a predetermine gap.
Furthermore, wiring substrate 8 has a film shape, where a plurality of wiring patterns (not shown) are formed on the upper and lower surfaces. Wiring substrate 8 has the back end sandwiched between the front end of upper substrate 1 and the front end of lower substrate 4. The back end of each wiring pattern of wiring substrate 8 is adhered and connected to the ends of upper electrodes 3A and 3B and the plurality of lower electrodes 6 with an anisotropically conductive adhesive (not shown) in which conductive particles are dispersed within the synthetic resin. The touch panel is configured in such a manner.
The touch panel configured in such a manner is arranged on the front surface of the display element such as a liquid crystal display element, and is attached to the electronic device. In this case, the pair of upper electrodes 3A and 3B and the plurality of lower electrodes 6 are electrically connected to an electronic circuit (not shown) of the electronic device through the plurality of wiring patterns of wiring substrate 8.
In the above configuration, when the area of arrow A at the upper surface of upper substrate 1 shown in FIG. 7 is pressed with a finger or a pen, for example, according to the display of the display element at the rear surface of the touch panel, upper substrate 1 bends and upper conductive layer 2 at the pressed area is brought into contact with lower conductive layer 5A.
In this case, a voltage is applied to both ends of upper conductive layer 2 through the plurality of wiring patterns of wiring substrate 8 from the electronic circuit. For instance, if a voltage of 5V is applied between upper electrodes 3A and 3B, a voltage of 2V is detected from lower conductive layer 5A and hence the position in the front and back direction of arrow A is detected by the electronic circuit by such a voltage.
At the same time, lower conductive layer 5A, from which the voltage is detected, is the third from the right in the plurality of lower conductive layers 5, for example, so that the position in the left and right direction of arrow A is detected by the electronic circuit. Therefore, the pressed position in the front and back direction and the left and right direction is detected by the electronic circuit, and switching of various functions of the device is carried out.
That is, if the upper surface of upper substrate 1 on a desired menu, for example the area of arrow A is pressed with a plurality of menus and the like displayed on the display element at the rear surface of the touch panel, the electronic circuit detects the pressed position in the front and back direction by the voltage detected from lower conductive layer 5A. The electronic circuit detects the pressed position in the left and right direction by lower conductive layer 5A of some order. Therefore, the selection of the desired menu that is pressed can be carried out from the plurality of menus.
In order to produce upper substrate 1 and lower substrate 4, for example, lower substrate 4, lower conductive layer 5 of thin film of indium tin oxide and the like is generally formed over the entire surface of the upper surface of lower substrate 4 through a sputtering method and the like as shown in a plan view of FIG. 9A.
The etching process is then carried out to remove the thin film of indium tin oxide in the unnecessary areas, so that a plurality of lower conductive layers 5 are formed to a substantially strip form on the upper surface of lower substrate 4, as shown in FIG. 9B.
Thereafter, the plurality of lower electrodes 6 made of silver, carbon, or the like extending from the front ends of lower conductive layers 5 to the front end of lower substrate 4 are formed, as shown in FIG. 9C, through screen printing, so that lower substrate 4 in which the plurality of lower conductive layers 5 and lower electrodes 6 are formed on the upper surface is completed.
As shown in FIG. 9C, the plurality of lower electrodes 6 are normally formed by straight portions 6A and 6B, which extend in a direction parallel to substantially strip-shaped lower conductive layer 5, and bent portion 6D coupled to straight portions 6A and 6B through arcuate portion 6C orthogonal thereto.
When forming such lower electrode 6 by screen printing, if the direction of screen printing is the direction of arrow B, straight portions 6A and 6B in the direction parallel thereto are subjected to a relatively satisfactory printing, but fading and blur, thickness variation and the like easily occur in bent portion 6D and arcuate portion 6C orthogonal thereto.
Therefore, bent portion 6D orthogonal to the direction of screen printing typically has the width made large to a certain extent compared to straight portion 6A and 6B to prevent such drawbacks.
For example, Unexamined Japanese Patent Publication No. 2007-310440 is known for citation list information related to the invention of this application.
However, in the conventional touch panel described above, the width of bent portion 6D and the like orthogonal to straight portions 6A and 6B of lower electrode 6 need to be formed large to a certain extent to prevent fading and blur, thickness variation, and the like at the time of screen printing of lower electrode 6 when producing lower substrate 4 formed with the plurality of lower conductive layers 5 and lower electrode 6. Thus, a so-called fine patterning in which the width and the gap of the plurality of lower electrodes 6 are reduced becomes difficult to carry out, and overall miniaturization becomes difficult to achieve.